REVIEW FOR CHAPTER 6 –
VOLCANOES
Where can we find volcanoes on
earth?
Most volcanoes are found near subduction zones and mid-ocean
ridges. This explains why the map of volcanoes on Earth matches
so well the map of tectonic plates. On the other hand, some
volcanoes are located in remote places like in the middle of the
Pacific plate (Hawaii), thousands of kilometres away from the
nearest plate boundary.
Before lava reaches the surface,
the molten material is called?
magma
Main hazards from a quiet
volcanic eruption is….
Lava flow
Sometimes rising magma is blocked
by horizontal layers of rock. The
magma forces the layer of rock to
bend upward into a landform called
Dome Mountain
Chapter 6 Volcanoes
Landforms From Lava and Ash
• Composite Volcanoes have quiet eruptions
that alternate with explosive eruptions,
forming layers of lava and ash.
Chapter 6 Volcanoes
Stages of Volcanic Activity
• Extinct volcanoes are considered “dead” meaning
that it is unlikely that they will erupt again
Chapter 6 Volcanoes
Stages of Volcanic Activity
• Dormant volcanoes are considered “asleep” or “sleeping
bears” meaning that they may become active in the future
Chapter 6 Volcanoes
Stages of Volcanic Activity
• Active volcanoes are considered “live” meaning that it is erupting, or
has shown signs that it may erupt in the near future
Chapter 6 Volcanoes
Magma Reaches Earth’s Surface
• Pyroclastic
flow is an
explosive
eruption that
includes hot
gases, cinders
(volcanic ash),
and bombs
(volcanic
rocks).
Chapter 6 Volcanoes
Magma Reaches Earth’s Surface
• Aa is a very thick, slow
moving lava. Aa contains high
amounts of silica, which gives
it it’s thickness. When aa
hardens, it forms a rough
surface consisting of jagged
(sharp) lava chunks.
Chapter 6 Volcanoes
Magma Reaches Earth’s Surface
• Pahoehoe is a very
thin, fast moving lava.
Pahoehoe contains
low amounts of silica,
which gives it it’s
thinness. When
Pahoehoe hardens, it
forms wrinkle and
rope-like rock
formations. Pahoehoe
is hotter than Aa.
Chapter 6 Volcanoes
Magma Reaches Earth’s Surface
• When a volcano
erupts, the force of
the expanding
gases pushes
magma from the
magma chamber
through the pipe
until it flows or
explodes out of the
vent.
Chapter 6 Volcanoes
Landforms From Magma
• Sills
Chapter 6 Volcanoes
Landforms From Magma
• Dikes
Chapter 6 Volcanoes
Landforms From Magma
• Volcanic Necks
Chapter 6 Volcanoes
Landforms From Magma
• Batholiths
Chapter 6 Volcanoes
Landforms From Lava and Ash
• Calderas are formed when a magma chamber
is emptied after an eruption and the volcano
mountain collapses into the empty space
creating a crater.
Crater Lake, Oregon
Chapter 6 Volcanoes
Landforms From Lava and Ash
• Lava Plateaus are formed from runny lava
(pahoehoe) that cools in flat sheets of rock.
Over time these layers form high plateaus.
Steamboat Rock,
Washington
Chapter 6 Volcanoes
Landforms From Lava and Ash
• Cinder Cone Volcanoes have explosive
eruptions of ash, cinders, and bombs that
form a cone-shaped hill.
Mount Etna, Italy
Chapter 6 Volcanoes
Landforms From Lava and Ash
• Shield Volcanoes have quiet eruptions and
have gentle slopes, which are not steep.